Process of making electron discharge device



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Patented Feb. 14, 1933 UNITED STATES PATENT OFFICE No Drawing.

This invention relates to process of making electron discharge devicesand more particularly to filaments used in connection with electrondischarge devices for radio and similar apparatus.

The objects of the invention are to provide a filament having a highelectron emission; to provide means for utilizing elements in substantially uncombined state which cannot ordinarily be handled becauseof oxidizing or otherwise combining with gases present in the air; toprovide means for overcoming an oxidized or similar coating in thefinished electron discharge device; to provide a coating on the filamentprior to placing the same in the electron discharge device which may bereadily removed from the filament after the filament is sealed withinthe electron discharge device; to provide a coating which will not onlybe removable but which will protect the filament against furtheroxidation and will reduce the oxide of the filament to its element orbase; to thus obtain a filament having maximum efiiciency with minimumdifficulty; to provide a filament and process of treating the same forrendering it effective after sealing in place in a bulb; to avoid thenecessity of applying a residual gas reducing agency to the plate; toemploy a coating on the filament for also reducing the residual gases inthe bulb; to obtain a reduction of the residual gases and removal of theoxidized coating at reduced temperature; to reduce losses fromunnecessary volatilization of the electron emissive substance or itsoxide; to also reduce losses from electrical defects, inactive filamentsand avoid unnecessary bombardment of the filament by positive ions ofgases present before reduction thereof; to secure simplicity ofconstruction of electron discharge devices, and to obtain otheradvantages and results as may be brought out in the followingdescription.

In carrying out my invention, I preferably employ an electron emissivefilament, as one instance of which I may mention a thoriated filament,although it is to be understood that there are other filaments which maybe also used. Generally speaking, electron emissive and especially theelement Application filed January 5, 1924. Serial No. 684,655.

thorium is, very easilyoxidized, and in fact, so easily oxidized thatmerely exposing the element to the atmosphere will result in itsbecoming coated with its oxide. The filament wire is usually in anoxidized state when received or ready for incorporation in an electrondischarge device, and my invention contemplates the utilization of suchoxidized filament, although it is to be understood that the inventionmay also be used in connection with filament which has not becomeoxidized.

The filament wire is first placed in a bulb of suitable size and shapewhich can be evacuated and sealed in which the filament may be given acoating. The coating which I prefer to apply is protective in its natureso that where the pure or substantially pure electron emissive elementis being used, the coating will prevent oxidation when the filament isagain exposed to the atmosphere.

The coating is also preferably of such a nature that it will be adaptedto subsequently reduce the oxide of the electron emissive element to itspure or substantially pure state. Within the said bulb, I preferablyinclude a piece of nickel or similar carrier having some magnesium onit. The magnesium is exploded that is, heated to such a point that itvaporizes and deposits on everything within the bulb, thus forming theprotective coating above mentioned upon the filament wire.

There area number of ways in which sufficient heating of this nickel orcarrier may be obtained for exploding the magnesium, and amongst thesevarious Ways may be mentioned the use of a pulsating current acting uponthe tube from the exterior thereof. Vhile various types of pulsatingcurrents may be employed satisfactorily, I have found that a fairly highaudio frequency pulsating current gives excellent results. It is to beunderstood also, that the action of this pulsating current upon thefilament wire is obtained without direct electrical contact therewith.As another means for heating the plate for exploding the magnesium, thecarrier or piece of nickel may be in the nature of a strip connected atits ends through the bulb toan exterior source of potential by whichmanufactured it has lihood of burning insufiicient emission sufficientcurrent may be applied for rendering the same incandescent. Other meansare known for accomplishing the same result and further descriptionthereof is considered unnecessary at this time. Sufiice it to say thatsuitable means have to be employed for heating the carrier or nickel forexploding the magnesium and it is within the scope of the invention toemploy means having direct contact or no contact as may be found mostdesirable. It may further be stated that because of the greater mass ofthe carrier or nickel,'it will become heated much more readily than thefilamentwhich has relatively little mass, and therefore the heating forexploding the magnesium will not have a bad effect upon the filament.

After the filament has become thus coated, the bulb is broken orotherwise removed and the filament is inserted in the tube of anelectron discharge device in the usual manner. After the operative partsof the electron discharge device are sealed within the tube, thefilament is lighted and the magnesium coating upon the filament reducesthe oxide of the electron emissive substances to a pure or substantiallypure state and also reduces the residual gases contained within thetube.

In electron discharge devices heretofore been necessary to obtainbombardment of the plate by the tungsten in the filament because of thefact that the exposed part of the thorium would not be in a pure orsubstantially pure state until after the magnesium was exploded, themagnesium *heretofore being upon the plate. It is to be noted in thepresent process that the magnesium is directly upon the filament and theelectron emission is obtained from the thorium or similar substancesshortly after the filament is lighted. Furthermore, the temperature towhich the filament has to be lighted in order to obtain this emission isvery much less, and in fact, may be estimated as g one-half of thetemperature to which the filament had to he lighted ess of explodingplate. Obviously,

under the old procthe magnesium from the I am thus enabled to produceelectron discharge devices with less like out the filament in theprocess of manufacture and reduce losses in a greater number of casesfrom what heretofore has been known as inactive filament. Under the oldprocess it often occurred that could be obtained from the tungsten toexplode the magnesium, although the filament might otherwise be inperfect condition. Under the present process, by utilizing magnesiumdirectly upon the filament, the proportion of electron discharge deviceswherein the filament is inactive is reduced very considerably. Thepresent process also obtains a greater amount of the oxidized electronemissive substances reduced than ,in the prior electron bombardmentmethod, because of the close association of the magnesium and itsresultant increased reducing effect upon the oxide of the filament inpreference to reduction by residual gases. Thus, in other words, I amenabled to obtain a filament of greater purity and having greaterelectron emissive qualities than when the magnesium is exploded from theplate.

It is to be understood that it is detrimental to a filament whereinvarious substances are used, to heat the filament to any temperaturewhich will have a tendency to volatilize the electron'emissivesubstances of the filament. In the use of thorium, as referred to in theprior description, as the electron emissive substance it is to be notedthat the thorium oxides are much more volatile than the tungsten andunder the old system necessitating raising the tungsten to a highertemperature for bombardment of the plate, there were large percentagesof losses of thorium and thorium oxide from the filament. Of course allof the thorium and thorium oxide lost from the filament means just thatmust less of the active electron emiss ve material and a less efficientdevice. Likewise, under the old method of bombardment of the plate bythe tungsten, the gases present in the tubes become ionized by theelectron emission from the filament, and having a relatively large massand traveling with considerable speed under the voltage applied andtherefore will strike the filament'with considerable force chipping offactive material with which the surface is coated. In the process of thepresent invention, the time interval during which the gases are presentprior to their reduction is comparatively very short, and therefore thelosses due to ch pping positive ions will be reduced to a minimum andthe filament will therefore be left with a greater amount of activematerial upon its surface.

7 As an additional feature of the present invention, it is observed thataging of the device is obtained while the other operations are inprocess upon the tube. In other words the filament may be lighted whilethe tube is on the pump or after the tube is finished. The filament islighted slowly and brought to the proper temperature gradually. I alsowish to point out at this time that the filament may be shaped eitherbefore or after has been treated or coated in the original bulb.

In constructing an electron discharge device in this manner, it will benoted that it is unnecessary to heat the plate therein as heretoforedone for exploding magnesium upon it, the magnesium being directlyvaporized or exploded by the filament. In this way, I enable a tube tobe manufactured and r..- sidual'gases reduced without any detrimentalefiect upon theplate such as warping, melting, etc. However, if sodesired magnesium may also be applied to the plate, and explodedsubsequent to exploding the magnesium on the filament. By exploding themagnesium on the filament first, the surface of the filament will becoated with electron emissive substance which can then bombard the platewith much less detrimental effect than has heretofore been possible.

Obviously detail changes and modifications may be made in themanufacture and use of my invention, and I do not wish to be understoodas limiting myself except as set forth in the following claims whenconstrued in the light of the prior art.

Having thus described my invention, I claim 1. A process ofmanufacturing filaments comprising incorporation of an electron emissivesubstance partially oxidlzed therein, and coating said filament bydepositing thereon by vaporization a quantity of mag nesium for reducingthe oxide of the electron emissive substance.

2. A filament comprising an electron emissive substance and its oxide,and a coat ng of vaporized magnesium on the filament for reducing thesame.

3. The process which comprises coating an electron emissive filament ina vacuum with a protective and reducing coating of magnesium, mountingsaid filament within a container, evacuating the container and flash ingthe coating by heating the filament simultaneously to reduce the oxidesin said filament, and to clean up residual gases Within the container.

4. The process of manufacturing an electron em ssive filament containingthorium and its oxide, which comprises vaporizing onto the filament acoating of magnesium while in one evacuated receptacle, removing themagnesium coated filament from the first receptacle and mounting it in asecond evacuatcd receptacle, and gradually heating the coated filamentto flash the magnesium while in said second receptacle.

5. The process of manufacturing an electron emissive filament containingan electron emissive substance with its oxide, which comprises mountingsaid filament in a first evacuated container and vaporizing onto saidfilament a coating of magnesium while in said container, removing saidcoated filament from the first container and mounting it in a secondevacuated container, and gradually heating the coated filament to causea chemical reaction between the coating and the filancnt while in saidsecond container to reduce the filament oxide.

6. The process of manufacturing an electron emissive filament whichcomprises incorporating in the filament an electron emissive substanceand its oxide, mounting the filament in a first evacuated container,vaporizing onto the filament a coating of magnesium while in saidcontainer, removing the coated filament from said container, and sealing it into an electron discharge device, and gradually heating thecoated filament to flash the magnesium while in the second evacuatedcontainer.

7. The process of manufacturing an electron emissive filament whichcomprises incorporating thorium and its oxide in said lament, mountingthe filament in an evacuated container, vaporizing onto the filament acoating of magnesium While in said container, removing the coatedfilament from said container and mounting it in an electron dischargedevice, and gradually heating the coated filament while in the electrondis charge device to secure a chemical reaction between the magnesiumcoating and the thorium oxide to render the filament electronicallyactive.

8. The process of manufacturinga metallic electron emissive filamentwhich comprises incorporating an electron emissive substance in saidfilament, vaporizing onto said filament in an evacuated container aquantity of magnesium to provide said filament with a protective coatingof the vaporized magnesium, removing said coated filament and mountingit in another evacuated container.

9. The process of manufacturing an electron emissive filament whichcomprises incorporating in said filament an electron emissive substance,placing the filament, together with a quantity of magnesium in a bulb,evacuating the bulb, depositing the magnesium by vaporization onto saidfilament, removing the filament from said bulb and mounting it inanother bulb, gradually heating said filament while in said other bulb,and simultaneously evacuating said other bulb to cause said coating toreduce the oxides existing on the filament.

10. An electron emitter comprising a thoriated filament having thereon acoating of vaporized magnesium.

FREDERICKL. HUNTER, JR.

